I think that's the mentality my pastor and music director have bought into, so we sing too many of those mediocre, overly repetitive "praise songs" every Sunday, even though the youth make up maybe 5-10% of the congregation.
BTW, I'm in my 20's and far prefer singing hymns in church instead of music that makes me feel like I'm listening to the local Christian radio station.
Our church is large enough that we have a specific youth service. It would definitely turn off most of the adults. I am just saying that to get the young (teen-age) interested the service must be upbeat. Then they are gradually matured into more traditional services.